There’s a fairly basic question at the core of the current food-stamp debate in Congress. Why has the program grown so rapidly over the past few years — to the point where 47 million Americans, one-sixth of the country, now receive food stamps?

Defenders of the program typically argue that enrollment rose because we had a horrific recession and unemployment hit the stratosphere. The Supplemental Nutrition Assistance Program (SNAP) is supposed to kick in to help families hit by economic distress. The program has kept 4.7 million people out of poverty. There’s no problem here. And so on.

Some conservatives, meanwhile, have emphasized that a big chunk of the increase is due to policy changes by Washington. In 2008, Congress allowed states to relax their standards for who could join the program. (Jobless adults could stay in the program if they lived in high-unemployment areas, for instance.) Then, as part of the 2009 stimulus bill, Congress temporarily boosted food-stamp benefits — the average benefit was $133 per month last year, although that increase expires this November.